1. Field
The present disclosure relates generally to telecommunications, and more particularly, to various concepts for reducing inter-carrier interference (ICI) an OFDM system.
2. Background
In recent years, there has been an increased interest in multi-carrier telecommunication systems. One example is a telecommunication system using Orthogonal Frequency Division Multiplexing (OFDM) technology. OFDM is a multi-carrier modulation technique that effectively partitions the overall system bandwidth into multiple sub-carriers. Data is modulated onto each sub-carrier by adjusting the sub-carrier's phase, amplitude or both. Typically, quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) is used, but other modulation schemes may also be used. These sub-carriers are spaced apart at precise frequencies to provide orthogonality, thereby eliminating crosstalk between the sub-carriers. This reduces the complexity of both the transmitter and receiver by eliminating the need for separate filters for each sub-channel typically required in Frequency Division Multiplexing (FDM) systems. Instead, efficient modulation and demodulation techniques may be employed using a Fast Fourier Transform (FFT) algorithm, making it ideal for low cost wideband communications. Today, OFDM is used in many telecommunication systems including Qualcomm's MediaFLO, Wireless Local Area Networks (WLAN), such as IEEE 802.11a, 802.11g, 802.16 (Wi-Max), IEEE 802.20 (Mobile Broadband Wireless Access), etc., Ultra wideband (UWB) systems, and others.
OFDM relies heavily on the transmitted sub-carriers being aligned with the demodulating sub-carriers at the receiver. An error in the receiver master clock frequency may cause the spacing of the demodulating sub-carriers to differ from those transmitted, resulting in a loss of orthogonality and introducing inter-carrier interference (ICI). Various solutions have been proposed in the past for reducing ICI in multi-carrier telecommunication systems. These solutions generally involve complex techniques to derive an error signal from the received signal to drive an Automatic Frequency Control (AFC) loop or perform some type of digital resampling process. Accordingly, there is a need in the art for more efficient means for reducing ICI in the multi-carrier telecommunication systems.